Process of tanning



Patented Nov. 5, 1935 ATN OFFICE PROCESS OF TANNING No Drawing.Application March 18, 1933, Serial No. 661,587

17 Claims.

The present invention relates to a tanning process and product, and moreparticularly to a process of tanning adapted to secure a white leather.

Heretofore, the attempt to obtain a white leather from cow and steerhides, calf, sheep, goat and the like have been unsatisfactory in theirresults for a number of reasons, among which are the following: Where analum or an alum formaldehyde tannage has been employed the skin has notbeen completely or permanently tanned, the tanning material being easilywashed out if such leather is exposed to water, and the skin or hidereturning in greater or less degree to its original untanned condition.

Where a chrome tannage is employed, and this is the common presentmethod of producing a white leather, it is necessary to subject thetanned leather to a further step or treatment, namely, the applicationof pigments to cover or overcome a distinct blue or green colorresulting from the tanning process. The pigment or pigments so applieddo not become a permanent part of the leather, being more or less in thenature of a coating, and when such pigmented leather has its surfaceremoved, or is cut or skived to present a raw edge or face, this willshow a very undesirable dirty bluish shade.

Oil tannage avoids the objection of lack of permanency or completenessof the tannage found with the alum formaldehyde tanning, and theobjectionable colors and the necessity of pigmentation present in thechrome tanning, but such oil tannage is a very long and slow process,requiring weeks for its completion.

I have found that a tungsten compound may be used as a tanning agent, incombination with other suitable reagents and under certain conditions,to quickly, completely, and permanently tan cowhides, calfskins,sheepskins and the like to a leather which not only possesses thecharacteristics necessary to adapt it for such uses as shoes, garments,gloves, etc., but which, when desired, may be of a permanent white colorboth on its surface and throughout its body.

The present invention consists in the process of tanning wherein acompound of tungsten is employed as a tanning agent and a completely andpermanently tanned leather is produced. This invention further consistsin the leather tanned by such process.

In practising the present invention, the preferred method is as follows:The skin or stock, such as cowhide, as it comes from the pickle, w chmay m e 2 of sulphuric acid and 6% of salt, will be given three washingsin the wheel with salt solution. This removes most of the uncombinedsulphuric acid from the skins. The wheel is then drained and a solutionof a tungsten compound is added. A satisfactory 5" at the end of whichtime an alum bath is added 7 slowly and at intervals for one hour. Asuitable alum bath consists of ten pounds of aluminum sulphate per onehundred pounds of stock or skins, dissolved in fifteen gallons of 5%sodium chloride solution. After the alum solution has been added thewheel is run for two hours longer, making three hours in all from thetime the first portion of the alum bath was added.

The mixed solution is then drawn off and the skins thoroughly washed inthe running water. They are now ready to be fat-liquored and. subjectedto the other usual steps or process to finish and prepare them forconsumption.

Instead of leaving the tungsten solution in the wheel and adding to itthe alum solutions, it may be desirable or convenient first to withdrawthe tungsten solution before addingthe alum.

While preferably the skins are first subjected to the tungstate liquorfor a substantial period of time, after which the alum bath is added,the process is not necessarily limited to this particular procedure ororder but may be practised otherwise within the scope of the appendedclaims.

In practising the above described process it is 4 essential that thehydrogen ion concentration (pH) be carefully controlled within fairlynarrow limits if a true tanning is to be effected. It has been foundthat with a pH value of from 3 to 4 and again slightly below 8 the bestresults are secured, giving a leather with a tungsten content in theform of oxides of from 14 to 18% by weight, although a satisfactoryleather may be obtained in which the tungsten content as calculated onthe basis of the tungstic oxide is only a portion of these amounts.

The process which is the subject of the present invention produces aleather which is permanently tanned by a tungsten compound; that is,tungsten in some form is combined with the 55 portion of the tungstenwill be lost upon washing. Where the tungsten compound, such as sodiumtungstate, is used in combination with aluminum sulphate, as abovedescribed, the leather will have not only a surface of pleasingwhiteness, but the same shade or color will be present throughout thebody of the leather so that all cut and skived edges have the same shadeor color as the adjacent surfaces.

Preferably the improved process will be practised in such a manner andwith such other ingredients or materials that a pleasing and uniformwhite color will be produced not only upon the surface of the leatherbut also extending throughout the body of the same. It is to beunderstood, however, that the invention is not necessarily so limitedfor .it comprehends in its broader aspects the use of a tungstencompound with materials and ingredients and a method of treatment topermanently and quickly tan the skin, irrespective of the color or shadeproduced.

Nor is the present invention limited to the use of a tungsten compoundas the sole and exclusive tanning reagent, but contemplates the use ofother tanning agents or materials simultaneously with, or proceeding, orfollowing the use of the tungsten compound. Thus the skins may be givena preliminary or partial tanning by means of chrome tanning materials,the tanning being completed by the action of the tungsten compound.

While the tungsten compound specifically referred to in the foregoingspecification has been sodium tungstate, it is to be understood that thepresent invention is not necessarily limited to this particular andspecific compound, as other compounds and forms of tunsten may 'beemployed as, for example, sodium paratungstate. Nor is the inventionlimited to the other specific ingredients or the particular proportionsexcept where so specifically set forth in the claims.

Having thus described the invention, what is claimed is:

1. The process of tanning skins which includes the step of subjectingthe skin to the action of a tungsten compound in acid solution, toeffect tanning of the skin.

2. The process of tanning skins to produce white leather which includesthe step of subjecting the skin to the action of a tungsten compound incombination with a salt and a weak acid, to effect tanning of the skin.

3. The process of tanning to produce white leather which consists ofsubjecting the skin to the action of a tungsten compound in acidsolution and an aluminum compound, to tan the skin.

4. The process of tanning to produce white leather which consists. ofsubjecting the skin to the action of sodium tungstate with acetic acidand thereafter to aluminum sulphate, to tan the skin.

5. The process of tanning to produce white leather which consists ofsubjecting the skin for a substantial period of time to the action of atungsten compound in acid solution, adding to said solution over asecond substantial period of time a second solution containing analuminum 4 fibres of the skin in such manner that no major compound andsubjecting the skin to the action of both solutions through said secondperiod of time, to tan the skin.

6. The process of tanning to produce white leather which includes thestep of subjecting the skin to the action of sodium tungstate, togetherwith sodium chloride, acetic acid, and aluminum sulphate, to tan theskin.

7. The process of tanning to produce white leather which consists insubjecting the skin to the action of sodium tungstate, sodium chloride,acetic acid, and aluminum sulphate, while controlling the hydrogen ionconcentration, to tan the skin.

8. As an article of manufacture, tanned leather having a compound oftungsten fixedly combined with the fibres thereof.

9. As an article of manufacture, leather having a compound of tungstenfixedly combined with a portion thereof in amount, calculated on thebasis of tungstic oxide, 14 to 18% of the weight of such portion.

10. As an article of manufacture, leather of white color on its surfaceand throughout its body and having a tungsten compound fixedly combinedwith its fibres as a tanning agent.

11. As an article of manufacture, leather containing a compound oftungsten combined in such a manner with the hide fibre that no majorportion of the tungsten compound will be lost upon washing.

12. The process of tanning skins which includes the step of subjectingthe skin to the action of a tungsten compound and effecting the fixationof the tungsten by controlling the pH at a point approximately from 3 to4.

13. The process of tanning skins which includes the step of subjectingthe skin to the action of a solution of a compound of tungsten with analkali and effecting the fixation of the tungsten by controlling the 3to 4.

14. The process of tanning skins which includes the step of subjectingthe skin to the action of an alkali tungstate, and effecting thefixation of the tungsten by controlling the pH at a point approximately3 to 4.

15. The process of tanning to produce white leather which consists insubjecting the skin to the action of a tungsten compound in solution andalum and eifecting the fixation of the tungsten by controlling the pH ata point approximately 3 to 4.

16. The process of tanning to produce white leather which consists insubjecting the skin to the action of a tanning agent to partially tanthe skin and thereafter subjecting the partially tanned skin to theaction of a tungsten compound and effecting the fixation of the tungstenby controlling the pH at a point approximately 3 to 4.

17. .The process of tanning to produce white leather which consists insubjecting the skin to the action of a plurality of tanning agents, eachhaving a tanning action on the skin, one of such tanning agents being acompound of tungsten, and effecting the fixation of the tungsten bycontrolling the pH at a point approximately 3 to 4.

pH at a point approximately HERMAN A. HERZOG.

